Pyrotherium ('fire beast') is an extinct genus of South American ungulate, of the order Pyrotheria, that lived in what is now Argentina and Bolivia, during the Late Oligocene. It was named Pyrotherium because the first specimens were excavated from an ancient volcanic ash deposit. Fossils of the genus have been found in the Deseado and Sarmiento Formations of Argentina and the Salla Formation of Bolivia.
So far, two valid species have been described, Pyrotherium romeroi, which lived in what it is today Argentina and P. macfaddeni from Bolivia, at the end of Oligocene. P. romeroi in particular is the most recent known pyrothere in the fossil record and best known for its fossil remains, which although incomplete are the best preserved in the entire order, indicating that they are also the largest, with an estimated body length from . It is also supposed to have developed a small trunk, but it is not related to the current elephants (proboscideans); the resemblance is so great that when studying the fossil remains, it was attributed in the past a relationship with elephants, although the true relationship of this herbivore is still controversial today.
Discovery and naming
The original remains of Pyrotherium, some molars, a premolar and an incisor, were originally identified in the Neuquén province in strata dating back to the late Oligocene epoch, identified by the Argentine naturalist Florentino Ameghino as couche à Pyrotherium (layers of Pyrotherium, in French) due to the presence of fossils of this animal that were the first to be identified there; these strata are now known as part of the Deseadan mammal-age (SALMA) in the area of the Deseado estuary, although there is the doubt whether the holotype of Pyrotherium romeroi really comes from Neuquén, it being possible that the remains actually came from Chubut. Ameghino considered that these areas corresponded to older terrains, from the Paleocene and even from the Cretaceous, because they were sent together with dinosaur remains; subsequent studies have shown that they actually come from the Oligocene, and in fact the Pyrotherium fossils have reached become the guide fossil of the late Oligocene. Because the remains of this animal originally appeared in the volcanic ash beds of the Deseado Formation, they gave rise to the name of the genus, which means "fire beast".
The name of the species P. romeroi is due to the captain of the Argentine army Antonio Romero who sent Ameghino the first known remains of the animal, although in several texts the erroneous spellings P. romeri or P. romerii has been used. Ameghino named several species from the Deseado area such as P. sorondoi based on partial remains, mainly teeth, but later studies indicated that they are part of a single species. The first relatively complete skull did not appear until the 20th century, being discovered by Frederic Brewster Loomis during the Amherst College expedition in 1911-1912, and listed as specimen ACM 3207.
Additional remains of the genus have appeared in Quebrada Fiera, from the Mendoza province (Argentina) and in Salla, in the department of La Paz in Bolivia; the latter consist of the remains of a partial jaw, fragments of skull bones, teeth, and some limb bone such as pieces of the humerus and astragalus, which were found between the 1960s and 1980s and were initially considered part of the species P. romeroi, and later they were classified as a different and smaller species, P. macfaddeni, whose species name is in honor of paleontologist Bruce J. MacFadden. Molar and postcranial bone remains found in sediments from the late Oligocene of Taubaté, Brazil were considered as a possible finding of Pyrotherium, but it is possible that they correspond to some different genus with which it is closely related, but not yet described.